Psychosocial events, such as the loss of or separation from a significant other, have been associated with a variety of psychiatric and medical disorders. Early childhood separation experiences often have long term consequences, such as adult depression, loneliness, and poor health. The reported increased morbidity and mortality could, in fact, be related to impairments in immunity. Herein, we propose to study, prospectively, the immediate and long term behavioral and immunological consequences of early social separation experiences and the role of social support in diminishing the impact of these experiences using a well-established animal model of loss, brief nonhuman primate mother-infant separation. A comprehensive immunological panel will include determination of in vitro mitogen-induced lymphocyte proliferation, enumeration of B cells, T cells, and T cell subsets, evaluation of natural killer cell cytotoxicity, measurement of the generation of specific antibodies and delayed hypersensitivity responses to Keyhole limpet hemacyanin, and assessment of phagocytosis. This panel assesses competency of both humoral and cell-mediated immunity with both in vivo and in vitro procedures. Panels will occur prior to, during, and following various social stressors (early maternal separation, entry into a new social group, exposure to novel stimuli and situations) and at three month intervals throughout a long term follow up period. Quantative behavioral observations will occur throughout the study period from early maternal separation until the completion of the prospective follow up study at 4 years of age. Control animals will undergo identical evaluations but without experiencing an early separation. Correlations will be made between the behavioral and immunological changes. The role of social support will be evaluated comparing the relative impact of maternal separation experiences in bonnet and pigtailed monkeys, two species with different social group structures. Bonnets tend to share care of young (high social support) whereas pigtailed monkeys do not (low social support). It is predicted that pigtailed infants will show greater behavioral and immunological changes during separation due to low support factors within their social group relative to bonnet monkeys. This project has important implications for an understanding of the immediate and long term behavioral and immunological correlates of early social separation experiences. These findings will significantly improve our understanding of the pathophysiology of grief and increased health risk among the recently bereaved.